Generally, a synthetic resin pipe is essentially established during public works such as electric and communication railroad line construction, waterway construction, or multiplex communications etc. Here, a wrinkle type pipe capable of properly expanding and contracting according to the change of ground status or the change of pressure of the conduit is widely used. A plurality of internal tubes smaller than the wrinkle type tube in diameter are built-in the wrinkle type tube and the optical cables are inserted into each internal conduits, thereby establishing the railroad line for multiple communication.
However, in the wrinkle type pipe having a plurality of internal tubes, since the internal tubes are manually assembled into the external tube of the wrinkle type pipe through separate extruding processes, the internal tubes are closely inserted into the external tube of the wrinkle type tube without an insertion space of the synthetic resin tube and the insertion length of the internal tube becomes longer. Accordingly, there are problems in that the productivity and quality thereof can be deteriorated.
In order to solve these problems, as shown in FIG. 1 and FIG. 2, Korean patent registration No. 10-0355751 discloses “Multi channel duct assembling body for cable” capable of connecting the internal tubes 1, which are coupled to the inside of the external tube 2, to each other by using connecting bands 3 and fusing the internal tubes to the external tube.
However, in case of the multi channel duct assembling body for cable as described above, as shown in FIG. 2, since the internal tubes made of a flexible material such as a polyethylene are not connected to each other, the internal tubes are extruded to the external tube 2 in a state that the internal tubes 1 are leaned to one side or deviated from the external tube 2. Accordingly, there is a big problem in that it is turned upon one side and a deformation is generated without inserting the internal tubes 1 into the inside of the external tube 2 at a predetermined interval and in a predetermined shape.
In addition to this, although the internal tubes 1 connected to each other through the connecting bands 3 are uniformly inserted into the inside of the external tube 2 to be fused, where the pipe made of the synthetic resin having long optical fibers or electrical wires or the like is installed in the ground, there is a problem in that it is exceedingly difficult to bend the internal tubes accommodated in the external tube.
In order to solve the above defect and problem, as shown in FIG. 1 and FIG. 2, Korean patent registration No. 10-0920476 filed by the present applicant discloses a synthetic resin tube with a plurality of internal tubes in that the plurality of the internal tubes, which is located at the inside of the external tube, is connected to each other through connecting portions, whereby it can prevent the coiled internal conduits from being unfolded owing to a strength of stability thereof and the entire portion or a part of a circumference surface of each internal tube is fused to the inner circumference surface of the external tube, whereby it can prevent the internal tubes from being twisted inside the external tube.
That is, as shown in FIG. 3, the synthetic resin tube with the plurality of internal tubes includes a synthetic resin external tube 10 molded by an extruding process, the plurality of synthetic resin internal tubes 20 molded by an extruding process and located at an inside of the synthetic resin external tube; and connecting portions 30 for connecting adjacent internal tubes 20 to each other, wherein looped curves or looped squares are formed through the plurality of internal tubes and the connecting portions in section and parts of each outer circumference of the internal tubes 20 are fused on an inner circumference of the external tube 10.
Therefore, since the plurality of the internal tubes 20 located inside the external tube 10 is connected to each other through the connection part, it can prevent the internal tubes 20 from being deviated to outside in case that the external tube 10 is damaged after the construction thereof. Also, the internal and external tubes can be molded through a series of extruding processes during manufacturing thereof and separate coiling or fixing works of the inner conduits can be eliminated, whereby easily manufacturing a multiple pipe type tube.
However, in case of the synthetic resin tube having the plurality of the internal tubes 20 as described above, since the side parts of each internal tube 20 are connected to each other in the shape of the looped curve through the connecting portions 30, when the internal tubes are inserted into and fused to the external tube, the elastic force of the connecting portions 30 for connecting the internal tubes 20 becomes weak. Accordingly, during the bending of the synthetic resin tube, there is a problem in that it is bent to a large load together with the plurality of the internal tubes 20, which is accommodated in the outer tube.